Just hours before his arrival, Mrs May defended the prince’s visit and Saudi’s involvement in Yemen at Prime Minister’s Questions.

Citing anti-terrorism co-operation between the UK and Saudi Arabia, Mrs May told MPs the link between the two countries is “historic, important and has saved the lives of potentially hundreds of people in this country”.

She added: “Their involvement in Yemen came at the request of the legitimate government of the Yemen, it is backed by the UN Security Council and as such we support it.”

Mrs May said she would raise humanitarian concerns over the three-year conflict which has left 22.2 million people dependent on food aid, according to UN figures.

Image:Save the Children placed a life-sized statue of a child outside parliament

The conflict began with a Saudi-led intervention to fight Iran-backed Houthi rebels.

Mrs May told MPs: “We are all concerned about the appalling humanitarian situation in Yemen and the effect that it is having on people, particularly women and children.”

Save the Children has installed a statue of a child near parliament to “draw attention to the violence that is being fuelled, in part, by British-made bombs”.

There are larger protests taking place on Wednesday evening, and demonstrators are planning to line up outside Downing Street when the prince leaves.

Saudi Arabia has bought advertising across London and in newspapers to welcome the prince to the country.

MBS is described as the power behind the throne of his father, King Salman.

Billed as “the prince of change” he has promised the most ambitious reform programme in Saudi’s history.